Pretensioning machine for making prestressed concrete bodies



3 Sheets-Sheet 1 INVENTOR A fro/vf vf Sept. 10, 1963 B. c. GERwlcK, JRv

PRETENsIoNING MACHINE EORMAKING PREsTREssED CONCRETE BODIES Filed June6, 1958 llmlmm-.H-h iv mW w Sept. 10, 1963 B, c. GERw1cK,JR 3,103,238

PREIENsIoNING MACHINE vEOE MAKING PREsIREssED CONCRETE BoDIEs Filed Junee, 195s s sheets-sheet 2 Sept. 10, 1963 B. C. GERWICK, JR

PRETENSIONING MACHINE FOR MAKING PRESTRESSED CONCRETE BODIES v FiledJune 6, 1958 PRICE-Q 5 sheets-shea s IN VEN TOR.

A TTOR/VEYS United States Patent 3,103,238 PRETENSIONIN G MACHDIE FORMAKING PRESTRESSED CONCRETE BODIES Ben C. Gerwick, ltr., Oakland,Calif., assigner to Ben C.

Gerwick, Inc., San Francisco, Calif., a corporation of California FiledJune 6, 1958, Ser. No. 740,245 3 Claims. (Cl. 14d-71) This inventionrelates generally to machines for positioning tensioned wires, cables,or like strands, preparatory to casting concrete bodies of theprestressed type.

In the past, various concrete bodies, such as slabs, beams, or the like,have been prestressed by casting the same about rods, cables, wires orother strands which have been tensioned. Machines have been proposed forpositioning the tensioned strands preparatory to the casting operation.One machine of this type makes use of a platform forming a casting area,and serving to mount pins over which the tensioned strands are engaged.The present invention pertains to machines of this type, and is animprovement over prior machines, particularly in that it makes possiblethe application of reinforcing strand tensioned by application ofrelatively high forces, thus making possible the manufacture ofprestressed concrete slabs, beams, or like bodies, which havereinforcement of adequate strength that is pretensioned to an optimumdegree.

Another object of the invention is to provide a machine `of the abovecharacter which facilitates maintaining high tensioning force upon thestrand, while at the same time facilitating the positioning of thetensioned strand to provide the desired location in the concrete body.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment has been setforth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

FIGURE l is a plan View schematically illustrating a machine inaccordance with the present invention.

FIGURE 2 is a side view schematically showing the machine of FIGURE l.

FIGURE 3 is a plan view illustrating a machine constructed in accordancewith FIGURES l and 2, and showing in particular the main and secondarycarriages.

FIGURE 4 is a `cross sectional view of the machine shown in FIGURE 3.

FIGURE 5 is a detail in section illustrating pin means for engaging thetensioned strands.

FIGURE 6 is a cross sectional view taken along the line 6-6 of FIGURE 5.

The machine illustrated in the drawing consists of a flat horizontalslab 10 which can be made of reinforced concrete, and which forms ahorizontal area for concrete casting operations. In conjunction with theslab 1t)l I provide strand feeding means including the main carriage 11,and the secondary carriage 12. Tracking means is provided for the maincarriagewhereby it may be moved in opposite directions over the slab1li. Additional tracking means is provided for the secondary carriage,whereby this carriage may be traversed laterally of the slab. While thedetails of the tracking means may vary, the construction illustrated forthe main carriage consists of curbs 14 extending along the sides of theslab 10, and serving to mount the parallel longitudinally extendingrails 16. Flanged wheels 17 carried by the main carriage, track upon therails.

The horizontal frame portion of the main carriage includes the trackingrails 18, which are engaged by the flanged Wheels 19 of the secondarycarriage 12.

As representative of suitable means for moving the main carriage, I haveshown lines 21 and 22, such as cables or chains, extending along thesides of the machine. They are shown anchored to the depending sideportions 23 and of the mainfcarriage frame, 'at points 24 and 25. A pairof winding drums 27 are rotatably mounted at one end of the slab 10, andare arranged to be reversibly driven by a motor 28 of the remote controltype. A pair of sheaves 29* are mounted at the other end of the slab.The line 22 is reeved over one of the corresponding sheaves 29, and thenextends alongside the slab, to the corresponding drum 27 upon which itis Wound. Each of the lines 21 likewise extends longitudinally of theslab to the corresponding drum 27, upon which it is oppositely wound.With this' arrangement, when the motor 28 is operated, lines 21 and 22move the main carriage in one direction or the other.

For moving the secondary carriage, a winding drum 31 is rotatablymounted upon one side of the main carriage, and is adapted kto be drivenin opposite directions by the reversible motor 32. A sheave 33` isrotatably mounted at the other end of the main carriage. Line 34 isanchored to one side of the secondary carriage, and extends to the drum31 upon which it is wound. Cable 36 is also anchored to the secondarycarriage and extends over the sheave 33, and then extends to the drum31, upon which it is oppositely w-ound. The circuit for energizing andcontrolling the motor 32 may include conventional trolley conductors andtraveling contactors (not shown).

In addition to the tracking means described above, the depending sidelframe portions 23 of the main carriage may be provided with rollers 37which engage the side rails 38.

FIGURE l schematically illustrates a reel 41 for supplying a cable,wire, or other reinforcing strand to the machine. Suitable journallingmeans (e.g. trunnions not shown) are provided for this. reel, and inaddition the reel is operatively coupled to means 42 ywhereby apredetermined torque can be applied to resist unwinding rotation. Suchtorque serves to apply a predetermined amount of tension to the strandas it i-s supplied to the machine. Means 42 may consist for example ofelectrical motive means of the adjustable torque type, or a steam enginecapable of applying a desired predetermined torque. Other torque devicesof the pneumatic and hydraulic type are available, and can be used forthis purpose.

It will be noted that the reel 41 is disposed olf one end of the machinewhereby the strand 43 extends in generally horizontal direction to thesecondary carriage 12. Preferably :suitable pull-equalizing means isprovided between the reel and the machine. Thus a loop of the strandextends downwardly from the stationary sheaves 44, and is engaged withthe vertically movable sheave 46. A weight 47 is carried by the sheave46, and is of such value as to apply the desired pull .to the strand 43.If' desired, suitable automatic control means can be employed to adjustthe torque of the means 42, in accordance with changes in the positionof the sheave 46.

The carriage 12 is provided with means whereby the tensioned strand isguided and applied to pins 51 or like means upon the slab 1G. Thus asshown particularly in FIGURE 4, sheaves 52 and 53 are mounted above andbelow the secondary carriage 12. The upper sheave isl carried by thesheave block 54, which is swivelled to turn about a vertical axis.V Asimilar sheave block 56 serves to mount the lower sheave 53, and thisblock is swivelled to the hollow str-ut or pipe 57, which extendsdownwardly fnom the frame of the secondary carriage. The tensionedreinforcing strand extends over sheave 52, downwardly through the hollowstrut 57, and then laterally in engagement with sheave 53.

The secondary carriage is shown provided with weights 3 55 which hold itupon the rails 18 against the pull applied to the strand 43.

The character of the pins 51 may depend upon the type of concretecasting operation desired. ment shown in lFIGURES 5 and 6 a pin section61 is set within a socket 62 provided in the slab 10. A second pinsection 63 is attached to section 61, by screw 64. The adjacent endfaces 66 and 67 of these pin sections are disposed at an angle to theaxis of the pin. The opening through pin section 63 for accommodatingscrew '64 is sufiiciently large whereby` when the two pin sections areclamped together, there is some off-setting in one direction as shown inFIGURE 5. A collar or sleeve 68 is positioned about each such pin, andis engaged by the tensioned reinforcing strand 43. The sleeve can bemade of various materials but should have suicient strength to withstandthe crushing effect of the strand. As will be apparent from FIGURES 5and 6 the off-setting of the pin is in a direction corresponding to thedirection of the component force applied to the sleeve 68 by thereinforcing strand. After a concrete body has been cast about thesleeves 68 and the reinforcing strand, and the concrete has hardened, itis a simple matter to remove the pin sections 63, thus freeing thesleeves 68.

Operation of my machine can be summarized as follows: The pins 51 areapplied to thel slab 10 in accordance with the desired reinforcementpattern. The reinforcing strand is reeved through the secondary carriageand anchored adjacent one end of the machine, as indicated at 71. Thetorque means 42 is placed in operation whereby constant tension ofpredetermined value is maintained on the reinforcing strand. Theoperator manipulates movements of the two carriages whereby the strandis applied progressively about the pins, as for example in the mannerillustrated in FIGURES l and 3. Thmoughout this operation pull is:maintained upon the strand whereby an optimum amount of pretensioningis applied. When this operation has been completed, the cable can be cutand anchored without relieving the tension, and thereafter suitableforms are applied to the slab, and the wet concrete mix is poured to thedesired form. After the concrete has hardened, the pins 51 aredisassembled and removed, and the cast body or bodies lifted from theslab.

In general, my machine greatly facilitates economic production ofprestressed slabs, beams and other concrete bodies. The machine isadaptable to a Wide variety of reinforcing patterns, as for examplepatterns used for prestressed beams where a large number of tensionedstrands extend longitudinally of the beam, and patterns employed forslabs or other shapes where it is desirable to extend lengths thetensioned reinforcement in two or more directions. The mounting of thereinforcing strand reel and the tensioning means, off to one end of themachine, greatly facilitates maintenance of the desired tensioningforces, particularly forces which are sufficient for relatively heavyreinforcing strands. Also it simplifies reel loading and unloadingoperations.

I claim:

l1. In a machine for positioning tensioned-reinforcing strandspreparatory to casting concrete bodies of substantially planarconfiguration, a bed forming a horizontal area upon which concretebodies can be cast, strand anchor means disposed adjacent said bed,fixed strand engaging elements disposed on said area, means feeding areinforcing strand 'to said horizontal area and spaced from said bed,said feeding means including a main carriage and a secondary carriage,means tracking the main carriage for movements in opposite directionslongitudinally of said area, means tracking the secondary carriage onthe main carriage for traversing movements in a direction lateral to thedirection of movement of the main carriage, means supplying thereinforcing strand under a predetermined tension between said strand'kanchor means In the arrange-` and said strand feeding means, said meanssupplying the strand being located apart from said carriages, and strandguiding means carried by the secondary carriage and serving to positionthe tensioned strand about said elements, said last means being movablein any direction over said area by movements of the main and secondarycarriages.

` 2. In a machine for positioning reinforcing strands preparatory tocasting concrete bodies of substantially planar configurations, a -bedforming a horizontal area upon which concrete bodies can be cast, strandanchor means disposed adjacent said bed, strand engaging elementsdisposed on said area, means feeding a reinforcing strand to saidhorizontal area and spaced from said bed, said feeding means including amain carriage and a secondary carriage, means for tracking the maincarriage for movements of the same in opposite directions longitudinallyof said area, means for tracking the secondary carriage on the maincarriage for traversing movements in a direction laterally of thedirection of movement of the main carriage, means supplying thereinforcing strand under predetermined tension between said strandanchor means and said strand feeding means, said means supplying thestrand being located apart from both said carlriages, a sheave on thecarriage over which the strand extending from said feed means isengaged, means mounting said sheave upon said carriage for permittingswinging movement of the sheave about a general ver-tical axis, a secondsheave disposed below the secondary carriage, rigid means mounted uponthe carriage and extending downwardly to said second sheave, and meansserving to mount said second sheave on said last named means whereby thesecond sheave is free to swing about a generally vertical axis, saidtensioned strand extending downwardly from the first sheave and thenoutwardly in a general horizontal direction in engagement with saidsecond sheave, fthe second sheave being movable in any direction oversaid area by movement of the main and secondary carriages.

3. In apparatus for positioning reinforcing strands preparatory tocasting concrete bodies of substantially planar configuration, a bedforming a horizontal area upon which concrete bodies can be cast, strandanchor means disposed adjacent said bed, strand engaging elements`disposed on said area, means feeding a reinforcing strand to saidhorizontal area and spaced from said bed, said feeding means including amain carriage and a secondary carriage, means for tracking the maincarriage for movements in opposite directions longitudinally of saidarea, means for tracking the secondary carriage on `the main carriagefor lateral horizontal traversing movements, means supplying reinforcingstrands under predetermined tension between said strand anchor means andsaid strand feeding means, said means for supplying reinforcing strandsbeing located off one end of said bed, and strand guiding means carriedby the secondary carriage and serving to position the tensioned strandabout said elements, said last means being movable in any direction oversaid area by movements of the main and secondary carriages.

References Cited in the file of this patent UNITED STATES PATENTS1,670,061 `Carroll May 15, 192s 1,823,680 Curtiss Sept. 15, 19311,846,767 Steuer Feb. 23, 1932 2,370,780 Crom Mar. 6, 1945 2,384,650vSjogren Sept. 1l, 1945 2,778,384 Regie et al. Ian. 22, 1957 2,785,866Vogt Mar. 19, 1957 2,855,159 Mallina IOCt. 7, 1958 2,862,670 IMallinaDec. 2, 19,58 3,020,937 lFryklund Feb. 13, 1962

1. IN A MACHINE FOR POSITIONING TENSIONED-REINFORCING STRANDSPREPARATORY TO CASTING CONCRETE BODIES OF SUBSTANTIALLY PLANARCONFIGURATION, A BED FORMING A HORIZONTAL AREA UPON WHICH CONCRETEBODIES CAN BE CAST, STRAND ANCHOR MEANS DISPOSED ADJACENT SAID BED,FIXED STRAND ENGAGING ELEMENTS DISPOSED ON SAID AREA, MEANS FEEDING AREINFORCING STRAND TO SAID HORIZONTAL AREA AND SPACED FROM SAID BED,SAID FEEDING MEANS INCLUDING A MAIN CARRIAGE AND A SECONDARY CARRIAGE,MEANS TRACKING THE MAIN CAR CARRIAGE FOR MOVEMENTS IN OPPOSITEDIRECTIONS LONGITUDINALLY OF SAID AREA, MEANS TRACKING THE SECONDARYCARRIAGE ON THE MAIN CARRIAGE FOR TRAVERSING MOVEMENTS IN A DIRECTIONLATERAL TO THE DIRECTION OF MOVEMENT OF THE MAIN CARRIAGE, MEANSSUPPLYING THE REINFORCING STRAND UNDER A PREDETERMINED TENSION BETWEENSAID STRAND ANCHOR MEANS AND SAID STRAND FEEDING MEANS, SAID MEANSSUPPLYING THE STRAND BEING LOCATED APART FROM SAID CARRIAGES, AND STRANDGUIDING MEANS CARRIED BY THE SECONDARY CARRIAGE AND SERVING TO POSITIONTHE TENSIONED STRAND ABOUT SAID ELEMENTS, SAID LAST MEANS BEING MOVABLEIN ANY DIRECTION OVER SAID AREA BY MOVEMENTS OF THE MAIN AND SECONDARYCARRIAGES.